Using alternative paths of descendant nodes for backhaul-link failure reporting in integrated access

ABSTRACT

A method, system and apparatus are disclosed. According to one or more embodiments, a child IAB node is configured to communicate with a first parent IAB node and a descendant IAB node over a backhaul network. The child IAB node includes processing circuitry configured to: detect a backhaul link failure between the child IAB node and the first parent IAB node; in response to the detected backhaul link failure, cause transmission of a radio link failure indication to the descendant IAB node; receive signaling indicating for the child IAB node to connect to a second parent IAB node; and modify network topology at least in part by connecting to the second parent IAB node.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Submission Under 35 U.S.C. § 371 for U.S. NationalStage Patent Application of International Application No.:PCT/EP2020/053641, filed Feb. 12, 2020 entitled “USING ALTERNATIVE PATHSOF DESCENDANT NODES FOR BACKHAUL-LINK FAILURE REPORTING IN INTEGRATEDACCESS,” which claims priority to U.S. Provisional Application No.62/805,015, filed Feb. 13, 2019, entitled “USING ALTERNATIVE PATHS OFDESCENDANT NODES FOR BACKHAUL-LINK FAILURE REPORTING IN INTEGRATEDACCESS,” the entireties of both of which are incorporated herein byreference.

TECHNICAL FIELD

The present disclosure relates to wireless communications, and inparticular, to recovery from a radio link failure in a backhaul network.

BACKGROUND

Integrated Access Backhaul Networks

The Third Generation Partnership Project (3GPP) is studying potentialsolutions for efficient operation of integrated access and wirelessaccess backhaul in New Radio (NR) (NR is also known as “5G”), referredto as the Integrated Access Backhaul (IAB) network.

IAB strives to reuse existing functions and interfaces defined foraccess. In particular, Mobile-Termination (MT), gNode B distributed unit(gNB-DU), gNB-Central Unit (CU), User Plane Function (UPF), Access andMobility Management Function (AMF) and Session Management Function (SMF)as well as the corresponding interfaces NR Uu (between MT and gNB), F1,NG, X2 and N4, are used as baselines for the IAB architectures.Modifications or enhancements to these functions and interfaces for thesupport of IAB will be explained in the context of the architecturediscussion. Additional functionality such as multi-hop forwarding isincluded in the architecture discussion as it may be helpful for theunderstanding of IAB operation and since certain aspects may requirestandardization.

The Mobile-Termination (MT) function has been defined as a component ofthe Mobile Equipment. In the context of this study, MT is referred to asa function residing on an IAB-node that terminates the radio interfacelayers of the backhaul Uu interface toward the IAB-donor or otherIAB-nodes.

FIG. 1 shows a reference diagram for IAB in standalone mode, whichcontains one IAB-donor and multiple IAB-nodes. The IAB-donor is treatedas a single logical node that includes a set of functions such asgNB-DU, gNB-CU-Control Plane (CP), gNB-CU-User Plane (UP) andpotentially other functions. In a deployment, the IAB-donor can be splitaccording to these functions, which can all be either collocated ornon-collocated as allowed by 3GPP Next Generation Radio Access Network(NG-RAN) architecture. IAB-related issues may arise when such split isexercised. Also, some of the functions presently associated with theIAB-donor may eventually be moved outside of the donor in case itbecomes evident that they do not perform IAB-specific tasks.

Few potential architectures to implement IAB have been identified (thereader is referred to 3GPP Technical Report (TR) 38.874 for the detailsof these architectures). These architectures are shown in FIGS. 2-6 .After analyzing the differences between these options during the studyitem phase of IAB specifications, the 3GPP has decided to standardizearchitecture 1 a for technical release-16. The proposed UP and CPprotocol stacks are shown in FIGS. 7 and 8 .

As shown above, the chosen protocol stacks reuse the currentCU-Distributed Unit (DU) split specification in 3GPP release-15, wherethe full F1-U (General Packet Radio Service Tunneling Protocol(GTP)-U/user datagram protocol (UDP)/Internet protocol (IP)) isterminated at the IAB node (like a normal distributed unit (DU)) and thefull F1-C (F1-application protocol (AP)/stream transmission controlprotocol (SCTP)/IP) is also terminated at the IAB node (like a normalDU). In the above cases, Network Domain Security (NDS) has been employedto protect both user plane (UP) and control plane (CP) traffic (IPsec inthe case of UP, and datagram transport layer security (DTLS) in the caseof CP). IPsec could also be used for the CP protection instead of DTLS.

One commonality between the CP and UP protocol stacks is that a newlayer, called an adaptation layer, has been introduced in theintermediate IAB nodes and the IAB donor, which is used for routing ofpackets to the appropriate downstream/upstream node. The adaptationlayer is also used for mapping the user equipment (UE) bearer data tothe proper backhaul radio link control (RLC) channel (and also betweenbackhaul radio link control (RLC) channels in intermediate IAB nodes) tosatisfy the end to end quality of service (QoS) requirements of bearers.

Some Examples of the Operation of the Transmitter and Receiver SideFollow.

Packet Data Convergence Protocol (PDCP)

The PDCP entity receives PDCP service data units (SDUs) from higherlayers and these SDUs are assigned a Sequence Number (SN) and deliveredto lower layers (i.e., RLC). The discard timer is also started at thetime a PDCP SDU is received. When the discard timer expires, the PDCPSDU is discarded and a discard indication is sent to lower layers. RLC,when possible, will then discard the RLC SDU.

In the receiver side, the PDCP entity starts the t-reordering when itreceives packets that are out of order. When the t-reordering expires,the PDCP entity updates the variable RX_DELIV which indicates the valueof the first PDCP SDU not delivered to the upper layers i.e., itindicates the lower side of the receiving window.

Radio Link Control (RLC)

In the transmitter side, when an RLC SDU is received from higher layers,a sequence number (SN) is associated to it. The transmitter may set thepoll bit to request the receiver side to transmit a status report. Whenthis is done, the t-poll Retransmit is started. Upon expiration of thistimer, the transmitter will again set the poll bit and may furtherretransmit those packet data units (PDUs) which were waiting to beacknowledged.

The receiver, on the other hand, will start the t-reassembly when RLCPDUs are not received in sequence. The function is similar to thet-reordering in PDCP. The timer is started when there is an SN gap,i.e., an RLC PDU is missing. When t-reassembly expires, for acknowledgemode (AM), the receiver will transmit a status report to trigger aretransmission in the transmitter side.

Media Access Control (MAC)

When the UE has data to be transmitted, it will request a grant by meansof the scheduling request (SR) or buffer status report (BSR).

Backhaul Link Failure

Backhaul Link Failure Recovery Scenarios

For various reasons, different scenarios of backhaul-link failure mayoccur in IAB networks. In the following, some example scenarios areillustrated for backhaul-link failure. Examples of such scenarios aredepicted with an illustrative figure (FIGS. 9-11 ) aimed at establishinga route between IAB-donor and IAB-node D after back haul (BH)-linkfailure, where:

-   -   Nodes A1 and A2 are IAB-donor nodes; nodes B to H are IAB-nodes;    -   The thin dashed lines represent the established connection        between two nodes;    -   The arrows represent the established route after BH-link        failure, and    -   the thick dashed line represents the new established connection.

Scenario A

In this scenario (depicted in FIG. 9 ), the backhaul-link failure occursbetween an upstream IAB-node (e.g., IAB-node C) and one of its parentIAB-nodes (e.g., IAB-node B), where the upstream IAB-node (IAB-node C)has an additional link established to another parent node (IAB-node E).

Scenario B

In this scenario (depicted in FIG. 10 ), the backhaul-link failureoccurs between an upstream IAB-node (e.g. IAB-node C) and all its parentIAB-nodes (e.g., IAB-nodes B and E). The upstream IAB-node (IAB-node C)has to reconnect to a new parent node (e.g., IAB-node F), and theconnection between IAB-node F and IAB-node C is newly established).

Scenario C

In this scenario (depicted in FIG. 11 ), the backhaul-link failureoccurs between IAB-node C and IAB-node D. IAB-node D has to reconnect tothe new IAB-donor (e.g., IAB-donor A2) via a new route.

Principal Steps of BH RLF Recovery in Architecture 1 a

In the following discussion, three scenarios of backhaul RLF andsubsequent recovery are discussed:

-   -   Scenario 1: Recovery via an existing BH link (FIGS. 12 and 13 ).    -   Scenario 2: Recovery via a newly established BH link using the        same IAB-donor CU (FIGS. 14 and 15 ).    -   Scenario 3: Recovery via a newly established BH link using a        different IAB-donor CU (FIGS. 16 and 17 ).

In scenario 1 (FIGS. 12 and 13 ), the MT on IAB-node-5 is dual-connectedto IAB-node-3 and IAB-node-4, which hold the master cell group (MCG) andthe secondary cell group (SCG), respectively. Two adaptation layerroutes have been established, one referred to as Adapt route A viaIAB-node-3, and the other referred to as Adapt route B via IAB-node 4.It is assumed that Adapt route A is used for backhauling of accesstraffic for the UE attached to IAB-node-5. The radio link failure (RLF)is further assumed to occur on the link to the MCG on IAB-node-3. TheSCG link to IAB-node-5 may further be in a radio resource control(RRC)-inactive state.

FIG. 13 shows one example for the recovery procedure for scenario 1:

-   -   1. The MT on IAB-node-5 conducts radio link monitoring (RLM) on        both links and discovers RLF on the link to MCG on IAB-node-3.    -   2. The MT may report MCG RLF over SCG radio resource control        (RRC) to the Central Unit (CU)-Control Plane (CP) using NR dual        connectivity (DC) procedures. This step implies that such        reporting is supported by NR DC. In case the SCG link is in RRC        inactive state, the MT will resume the RRC connection on this        link.    -   3. The CU-CP migrates the MT's MCG from IAB-node-3 to IAB-node-4        using NR DC procedures. This step implies that such procedure is        supported by NR DC.    -   B. The CU-CP migrates the F1*-U connection with the distributed        unit (DU) on IAB-node-5 to Adapt route B. It further uses Adapt        route B for F1*-C signaling with the DU on IAB-node-5. This step        also has to be applied to all descendent IAB-nodes of        IAB-node-5.    -   C. The CU-CP may release Adapt route A.

After backhaul (BH) RLF recovery, the CU-CP can add topologicallyredundant BH links and routes. Note that while the Scenario 1 recoveryprocedure is presented for the case of multi-connectivity of single-MTIAB-nodes, it is expected that a similar solution is applicable to thecase of multi-connected multi-MT IAB-nodes.

In scenario 2 (FIGS. 14 and 15 ), the MT on IAB-node-5 is singlyconnected to IAB-node-3. One adaptation layer route has been establishedvia IAB-node-3 referred to as Adapt route A. The RLF is assumed to occuron the link between IAB-node-5 and its parent node IAB-node-3.

FIG. 15 shows one example of the recovery procedure for scenario 2:

-   -   1. The MT on IAB-node-5 conducts RLM on the link to its parent        and discovers the RLF.    -   2. The MT on IAB-node-5 synchronizes with the DU on IAB-node-4        and performs a random access channel (RACH) procedure.    -   3. The MT on IAB-node-5 initiates        RRC-Connection-Reestablishment, leveraging existing NR        procedures. Since the central unit (CU) is the same as before,        it has all the context of this MT. IAB-node-5 discovers that the        CU has not changed through a CU-specific identifier provided to        the MT. Consequently, IAB-node-5's DU can keep the existing        F1-application protocol (AP) with the CU.    -   A. The CU-CP establishes Adapt route B to IAB-node-5 via        IAB-donor DU2, IAB-node-2 and IAB-node-4.    -   B. The CU-CP migrates F1*-U with the DU on IAB-node-5 to Adapt        route B. It further uses Adapt route B for F1*-C signaling with        the DU on IAB-node-5. This step also should be applied to all        descendent IAB-nodes of IAB-node-5.    -   C. The CU-CP may release Adapt route A.

After BH RLF recovery, the CU-CP can add topologically redundant BHlinks and routes.

In scenario 3 (FIGS. 16 and 17 ), the MT on IAB-node-5 issingle-connected to IAB-node-3. One adaptation layer route has beenestablished via IAB-node-3 referred to as Adapt route A. The RLF isassumed to occur on the link between IAB-node-5 and its parent nodeIAB-node-3.

FIG. 17 shows one example for the recovery procedure for scenario 3:

-   -   1. The MT on IAB-node-5 conducts RLM on the link to its parent        and discovers RLF.    -   2. The MT on IAB-node-5 synchronizes with the DU on IAB-node-4        and performs a random access channel (RACH) procedure.    -   3. The DU on IAB-node-5 discontinues service since it has lost        F1*-C connectivity to gNB-CU-1.    -   4. The MT on IAB-node-5 initiates        RRC-Connection-Reestablishment, leveraging existing NR        procedures. Since the CU is different, it may or may not be able        to fetch the context of this MT. IAB-node-5 discovers that the        CU has changed from a CU-specific identifier provided to the MT.        Consequently, IAB-node-5 has to restart F1-AP from its DU to the        new CU.    -   A. The new CU-CP establishes Adapt route B to IAB-node-5 via        IAB-donor DU2, IAB-node-2 and IAB-node-4.    -   B. The DU on IAB-node-5 initiates a new F1*-C connection to the        new CU-CP. This procedure is the same as IAB-node setup phase        2.2 described in section 9.3 of 3GPP Technical Report (TR)        38.874. The DU will obtain a new configuration during that        procedure, e.g., a new physical cell identity (PCI). After that,        the DU resumes service.    -   5. The UE determines RLF with the prior DU entity on IAB-node-5.    -   6. The UE discovers and selects the new DU entity on IAB-node-5.    -   7. The UE conducts a random access procedure with this new DU        entity on IAB-node-5.    -   8. The UE initiates RRC-Connection-Reestablishment with the new        CU-CP, leveraging NR procedures. The new CU-CP may or may not be        able to fetch the UE's context from the old CU-CP. The new CU-CP        will set up F1*-U for the UE with the new DU on IAB-node-5        following NR procedures.    -   C. The CU-CP releases Adapt route A. This release may be based        on F1*-C failure detection.

After BH RLF recovery, the CU-CP can add topologically redundant BHlinks and routes.

Steps 3, 4, A, B, C and potentially steps 1 and 2 also may have to beapplied by all descendant IAB-nodes of IAB-node-5. Further, steps 4, 5and 6 may also be applied by all UEs connected to descendant IAB-nodesof IAB-node-5.

As these steps show, the BH RLF recovery procedure via a new backhaullink with a different CU may cause multiple subsequent RLFs fordescendant IAB-nodes and UEs. This may cause long service interruptionfor UEs. Further enhancements may be needed to reduce this serviceinterruption.

Downstream Notification of BH RLF in Architecture 1 a

When the IAB-node observes RLF on its parent link, it cannot providefurther backhaul service to downstream IAB-nodes. Also, child IAB-nodescannot further serve their descendant IAB-nodes. One example is shown inFIG. 18 , where IAB-node-5 observes RLF in the link to its parentIAB-node-3 and subsequently cannot provide backhaul service to its childnode, i.e., IAB-node-6.

While the IAB-node observing RLF is aware about backhaul connectivityloss, the descendent IAB-nodes do not have explicit means to identifythis upstream backhaul connectivity loss. In case the RLF can berecovered swiftly, as can be expected for BH-RLF-recovery scenario 1,there may be no need to explicitly inform the descendant IAB-nodes aboutthe temporary BH connectivity loss. When the BH RLF cannot be recoveredswiftly, it may be beneficial to release backhaul connectivity todescendant IAB-nodes so that they themselves can seek means to recoverfrom the BH RLF. For this purpose, three options may be considered:

-   -   Option 1: The IAB-node DU discontinues service. Consequently,        the child nodes will also determine BH RLF and follow through        the above procedures to recover its link to the backhaul        network.    -   Option 2: The IAB-node DU explicitly alerts child IAB-nodes        about the upstream RLF. Child IAB-nodes receiving this alert can        forward the alert further downstream. Each IAB-node receiving        such alert initiates BH-RLF recovery as discussed above.    -   Option 3: Every IAB-node can regularly share information on,        e.g., BH quality, to its child or parent IAB-nodes. In this        manner, downstream or upstream RLF can be sensed without taking        explicit actions.

In case a descendant IAB-node (such as IAB-node 6) can recover from suchan upstream RLF by using one of the procedures described above, its DUcan provide BH RLF-recovery for former ancestor nodes (such as IAB-node5).

Efficient Backhaul Link Failure Recovery

The recovery procedure for backhaul failure scenarios 2 and 3 includesidentifying an alternate parent node and establishing/re-establishingthe control plane and user plane through the alternate parent node.However, identifying and attaching to an alternate node can take asignificant amount of time and also may not always be possible, e.g.,due to lost connectivity with the donor CU or due to lack of alternativeparent nodes (especially in millimeter-wave deployments). It may beuseful to consider how the IAB network is reorganized when there is abackhaul failure in a way that minimizes interruption time of connectionwith the IAB-donor.

FIG. 19 illustrates a scenario of a backhaul failure on one of the linksin an IAB network. In such scenarios, many IAB-nodes and UEs may be leftwithout a connection to the IAB-donor and may need to find alternateparent nodes. Downstream IAB-nodes (e.g., IAB-nodes 4, 6 in FIG. 19 )and the IAB-donor may need to be informed of the backhaul failure.Furthermore, if all the affected IAB-nodes simultaneously try to findalternate parent nodes, the resulting topology may be inefficient.

The following can be considered for recovery from backhaul failures:

-   -   Information can be provided to downstream IAB-nodes regarding        backhaul failure including a list of nodes that cannot serve as        parent nodes due to the backhaul failure.    -   Preparation of alternative backhaul links and routes in advance        (i.e., before occurrence of RLF).

As discussed above, there are different backhaul failure scenarios anddifferent mechanisms to recover from them. The problem is furtherillustrated in FIG. 20 , where several IAB nodes may be leftdisconnected from the IAB-donor (Node A1) due to a failure of a backhaullink on the path to the donor where IAB nodes B, C, D, K, N and P may beconsidered to be on an established communication path to donor IAB nodeA1 while other nodes such as IAB node O, H, J, etc. are not on thisestablished communication path. For the scenario shown in FIG. 16 , thefailure of the backhaul link of IAB node C may cause the descendantnodes of IAB node C (D, K, N, and P) to be disconnected as well.

As discussed above, mechanisms are already proposed where the affectedIAB node (i.e. node C) can send indications to its descendant IAB nodes.The descendant IAB nodes can then try to find alternate parent nodes.However, this may lead to a chaotic situation where several nodes aretrying to find alternate paths and increases the overall signaling load(and also several UEs may end up being impacted, as data flow may beinterrupted during the path switching of all these IAB nodes).

In the failure recovery scenarios described above, it may always be theaffected IAB node (i.e. node C) that initiate reconnection with theIAB-donor by employing either existing connections to establish the newroute or new alternate parent nodes/paths had to be established toenable the new path. However, in some situations, this process(identifying and attaching to alternative parent node) can take asignificant amount of time and may even not be possible due tounavailability of alternative parent node(s). On the other hand, some ofthe affected descendant nodes (e.g. nodes D, K, and P shown in FIG. 20 )can have alternate paths to the IAB-donor.

SUMMARY

Some embodiments advantageously provide methods, systems, andapparatuses for recovery from a radio link failure in a backhaulnetwork.

Methods to be performed by an IAB node (as referred to as a first IABnode in one or more embodiments and/or examples) upon detecting a linkfailure in its backhaul link to its parent IAB node are proposed:

-   -   The IAB node sends an indication to a subset of its child IAB        nodes that its backhaul link has failed.        -   This can be done in a dedicated manner (i.e., one by one to            each child IAB node via a MAC CE, PDCP control PDU, etc.) or            broadcast (e.g., in a SIB, system information block).        -   The receiving nodes can use the information to pause or            throttle (e.g. reduce data transmission).    -   The indication can include a report that is to be forwarded to        the donor CU        -   The report can be sent also in a separate message than the            first indication        -   The report can contain information such as the reason for            the link failure, latest measurement reports from the first            IAB node. etc.    -   If a child IAB node has an alternate path to the donor, the        child IAB forwards that information towards the CU via that        path.        -   If not, the child IAB node can pass the report to its            children and the process is repeated hierarchically.    -   When the CU receives the report, it may use the information        contained therein (i.e. measurement report), to decide the best        alternate parent for the IAB node        -   The CU prepares an RRC Reconfiguration message to the IAB            node        -   The CU sends it to the child node that has forwarded the            failure report    -   The child IAB node, upon getting the RRC reconfiguration message        from the CU, may forward it to the first IAB node    -   The first IAB node applies the RRC reconfiguration and connects        to the target indicated in the reconfiguration message.

According to one aspect of the disclosure, a child integrated accessbackhaul (IAB) node configured to communicate with a first parent IABnode and a descendant IAB node over a backhaul network is provided. Thechild IAB node includes processing circuitry configured to: detect abackhaul link failure between the child IAB node and the first parentIAB node; in response to the detected backhaul link failure, causetransmission of a radio link failure indication to the descendant IABnode; receive signaling indicating for the child IAB node to connect toa second parent IAB node; and modify network topology at least in partby connecting to the second parent IAB node.

According to one or more embodiments of this aspect, the radio linkfailure indication is configured to cause each descendant IAB node in anestablished communication path receiving the radio link failureindication to modify data transmission and remain on the establishedcommunication path to the child IAB node. According to one or moreembodiments of this aspect, the modifying of data transmission includeslimiting at least one of a packet data convergence protocol, PDCP,process, radio link control, RLC, process and medium access control,MAC, process. According to one or more embodiments of this aspect, themodifying of data transmission includes one of: at least temporarilypausing data transmission; and at least temporarily reducing a datatransmission rate. According to one or more embodiments of this aspect,the transmission of the radio link failure indication to the descendantIAB node includes one of broadcasting the radio link failure indicationto the descendant IAB node and transmitting the radio link failureindication to the descendant IAB node via dedicated signaling.

According to one or more embodiments of this aspect, the radio linkfailure indication is a failure report that indicates at least one of: acause of the detected backhaul link failure; IAB node identification;failure report identifier; backhaul link failure time; and results ofmeasurements performed by the child IAB node. According to one or moreembodiments of this aspect, the radio link failure indication is afailure report that includes results of measurements performed by thechild IAB node where the results of the measurements indicate at leastone discoverable parent IAB node. According to one or more embodimentsof this aspect, the signaling is RRC signaling that is received from thedescendant IAB node where the RRC signaling includes an RRCreconfiguration message.

According to another aspect of the disclosure, a method implemented by achild integrated access backhaul (IAB) node that is configured tocommunicate with a first parent IAB node and a descendant IAB node overa backhaul network is provided. A backhaul link failure between thechild IAB node and the first parent IAB node is detected. In response tothe detected backhaul link failure, transmission is caused of a radiolink failure indication to the descendant IAB node. Signaling indicatingfor the child IAB node to connect to a second parent IAB node isreceived. Network topology is modified at least in part by connecting tothe second parent IAB node.

According to one or more embodiments of this aspect, the radio linkfailure indication is configured to cause each descendant IAB node in anestablished communication path receiving the radio link failureindication to modify data transmission and remain on the establishedcommunication path to the child IAB node. According to one or moreembodiments of this aspect, the modifying of data transmission includeslimiting at least one of a packet data convergence protocol, PDCP,process, radio link control, RLC, process and medium access control,MAC, process. According to one or more embodiments of this aspect, themodifying of data transmission includes one of: at least temporarilypausing data transmission; and at least temporarily reducing a datatransmission rate. According to one or more embodiments of this aspect,the transmission of the radio link failure indication to the descendantIAB node includes one of broadcasting the radio link failure indicationto the descendant IAB node and transmitting the radio link failureindication to the descendant IAB node via dedicated signaling. Accordingto one or more embodiments of this aspect, the radio link failureindication is a failure report that indicates at least one of: a causeof the detected backhaul link failure; IAB node identification; failurereport identifier; backhaul link failure time; and results ofmeasurements performed by the child IAB node.

According to one or more embodiments of this aspect, the radio linkfailure indication is a failure report that includes results ofmeasurements performed by the child IAB node where the results of themeasurements indicates at least one discoverable parent IAB node.According to one or more embodiments of this aspect, the signaling isRRC signaling that is received from the descendant IAB node where theRRC signaling includes an RRC reconfiguration message.

According to another aspect of the disclosure, a donor integrated accessbackhaul (IAB) node in communication with a first parent IAB node, achild IAB node and at least one descendant IAB node over a backhaulnetwork is provided. The first parent IAB node is in communication withthe child IAB node and the descendant IAB node. The donor IAB nodeincludes processing circuitry configured to: receive a radio linkfailure indication from one of the at least one descendent IAB nodeswhere the radio link failure indication indicates a radio link failurebetween the child IAB node and the first parent IAB node; determine asecond parent IAB node for the child IAB node to connect to based atleast in part on the radio link failure indication; and causetransmission of signaling to the child IAB node, the signalingindicating for the child IAB node to modify a network topology at leastin part by connecting to the second parent IAB node.

According to one or more embodiments of this aspect, the radio linkfailure indication is configured to cause each descendant IAB node in anestablished communication path receiving the radio link failureindication to modify data transmission and remain on the establishedcommunication path to the child IAB node. According to one or moreembodiments of this aspect, the modifying of data transmission includeslimiting at least one of a packet data convergence protocol, PDCP,process, radio link control, RLC, process and medium access control,MAC, process. According to one or more embodiments of this aspect, themodifying of data transmission includes one of: at least temporarilypausing data transmission; and at least temporarily reducing a datatransmission rate.

According to one or more embodiments of this aspect, the radio linkfailure indication is a failure report that indicates at least one of: acause of the detected backhaul link failure; IAB node identification;failure report identifier; backhaul link failure time; and results ofmeasurements performed by the child IAB node.

According to one or more embodiments of this aspect, the radio linkfailure indication is a failure report including results of measurementsperformed by the child IAB node, the results of the measurementsindicating at least one discoverable parent IAB node. According to oneor more embodiments of this aspect, the signaling is RRC signaling thatincludes an RRC reconfiguration message. According to one or moreembodiments of this aspect, the at least one descendant IAB node is aplurality of descendant IAB nodes.

According to another aspect of the disclosure, a method implemented by adonor integrated access backhaul (IAB) node that is in communicationwith a first parent IAB node, a child IAB node and at least onedescendant IAB node over a backhaul network is provided. The firstparent IAB node is in communication with the child IAB node and thedescendant IAB node. A radio link failure indication from one of the atleast one descendent IAB node is received. The radio link failureindication indicates a radio link failure between the child IAB node andthe first parent IAB node. A second parent IAB node for the child IABnode to connect to is determined based at least in part on the radiolink failure indication. Transmission of signaling to the child IAB nodeis caused. The signaling indicates for the child IAB node to modify anetwork topology at least in part by connecting to the second parent IABnode.

According to one or more embodiments of this aspect, the radio linkfailure indication is configured to cause each descendant IAB node in anestablished communication path receiving the radio link failureindication to modify data transmission and remain on the establishedcommunication path to the child IAB node. According to one or moreembodiments of this aspect, the modifying of data transmission includeslimiting at least one of a packet data convergence protocol, PDCP,process, radio link control, RLC, process and medium access control,MAC, process. According to one or more embodiments of this aspect, themodifying of data transmission includes one of: at least temporarilypausing data transmission; and at least temporarily reducing a datatransmission rate.

According to one or more embodiments of this aspect, the radio linkfailure indication is a failure report that indicates at least one of: acause of the detected backhaul link failure; IAB node identification;failure report identifier; backhaul link failure time; and results ofmeasurements performed by the child IAB node. According to one or moreembodiments of this aspect, the radio link failure indication is afailure report including results of measurements performed by the childIAB node where the results of the measurements indicates at least onediscoverable parent IAB node. According to one or more embodiments ofthis aspect, the signaling is RRC signaling that includes an RRCreconfiguration message. According to one or more embodiments of thisaspect, the at least one descendant IAB node is a plurality ofdescendant IAB nodes.

According to another aspect of the disclosure, a descendant integratedaccess backhaul (IAB) node in communication with a donor IAB node via atleast a first parent IAB node and a child IAB node over a backhaulnetwork is provided. The descendant IAB node includes processingcircuitry configured to: receive a radio link failure indication; inresponse to the radio link failure indication: modify data transmissionand remain on an established communication path to the child IAB node;and cause transmission of the radio link failure indication to the donornode; receive signaling from the donor IAB node, the signalingindicating for the child IAB node to modify network topology at least inpart by connecting to a second parent IAB node; and cause transmissionof the signaling to the child IAB node.

According to one or more embodiments of this aspect, the processingcircuitry is further configured to: determine whether an alternatecommunication path from the descendant IAB node to the donor IAB node isconfigured; and if the alternate communication path is configured,transmit the radio link failure indication along the alternativecommunication path to the donor IAB node. According to one or moreembodiments of this aspect, the processing circuitry is furtherconfigured to: determine whether an alternate communication path fromthe descendant IAB node to the donor IAB node is configured; and if thealternate communication path is not configured, cause transmission ofthe radio link failure indication to another descendant IAB node.According to one or more embodiments of this aspect, the modifying ofdata transmission includes one of: at least temporarily pausing datatransmission; and at least temporarily reducing a data transmissionrate.

According to one or more embodiments of this aspect, the modifying ofdata transmission includes limiting at least one of a packet dataconvergence protocol, PDCP, process, radio link control, RLC, processand medium access control, MAC, process. According to one or moreembodiments of this aspect, the radio link failure indication is afailure report destined for a donor IAB node where the failure reportindicates at least one of: a cause of the radio link failure; IAB nodeidentification; failure report identifier; backhaul link failure time;and results of measurements performed by the child IAB node. Accordingto one or more embodiments of this aspect, the radio link failureindication is a failure report destined for a donor IAB node where thefailure report includes results of measurements performed by the childIAB node where the results of the measurements indicate at least onediscoverable parent IAB node.

According to one or more embodiments of this aspect, the signaling isRRC signaling that includes an RRC reconfiguration message. According toone or more embodiments of this aspect, the descendant IAB node is oneof: a logically next hop from the first parent IAB node; and at leasttwo logical next hops from the first parent IAB node.

According to another aspect of the disclosure, a method implemented by adescendant integrated access backhaul (IAB) node that is incommunication with a donor IAB node via at least a first parent IAB nodeand a child IAB node over a backhaul network is provided. A radio linkfailure indication is received. In response to the radio link failureindication: data transmission is modified and the descendant IAB noderemains on an established communication path to the child IAB node.Transmission of the radio link failure indication to the donor IAB nodeis caused. Signaling from the donor IAB node is received where thesignaling indicating for the child IAB node to modify network topologyat least in part by connecting to a second parent IAB node. Transmissionof the signaling to the child IAB node is caused.

According to one or more embodiments of this aspect, a determination isperformed whether an alternate communication path from the descendantIAB node to the donor IAB node is configured, and if the alternatecommunication path is configured, transmission of the radio link failureindication along the alternative communication path to the donor IABnode is caused. According to one or more embodiments of this aspect, adetermination is performed whether an alternate communication path fromthe descendant IAB node to the donor IAB node is configured. If thealternate communication path is not configured, transmission of theradio link failure indication to another descendant IAB node is caused.According to one or more embodiments of this aspect, the modifying ofdata transmission includes one of at least temporarily pausing datatransmission, and at least temporarily reducing a data transmissionrate.

According to one or more embodiments of this aspect, the modifying ofdata transmission includes limiting at least one of a packet dataconvergence protocol, PDCP, process, radio link control, RLC, processand medium access control, MAC, process. According to one or moreembodiments of this aspect, the radio link failure indication is afailure report destined for a donor IAB node where the failure reportindicates at least one of: a cause of the radio link failure; IAB nodeidentification; failure report identifier; backhaul link failure time;and results of measurements performed by the child IAB node. Accordingto one or more embodiments of this aspect, the radio link failureindication is a failure report destined for a donor IAB node where thefailure report includes results of measurements performed by the childIAB node and where the results of the measurements indicating at leastone discoverable parent IAB node. According to one or more embodimentsof this aspect, the signaling is RRC signaling that includes an RRCreconfiguration message.

According to one or more embodiments of this aspect, the descendant IABnode is one of: a logically next hop from the first parent IAB node; andat least two logical next hops from the first parent IAB node.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present embodiments, and theattendant advantages and features thereof, will be more readilyunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings wherein:

FIG. 1 is a reference diagram for Integrated Access Backhaul (IAB) in astandalone mode;

FIGS. 2-6 illustrate architectures to implement IAB identified by the3GPP;

FIGS. 7 and 8 illustrate user plane (UP) and control plane (CP) protocolstacks for the standardized architecture shown in FIG. 2 ;

FIGS. 9-11 illustrate example scenarios for backhaul (BH) link failure;

FIGS. 12 and 13 illustrate recovery via an existing BH link;

FIGS. 14 and 15 illustrate recovery via a newly established BH linkusing the same IAB donor central unit (CU);

FIGS. 16 and 17 illustrate recovery via a newly established BH linkusing a different IAB donor CU;

FIG. 18 illustrates an IAB node observing radio link failure (RLF) onits parent link;

FIG. 19 illustrates a scenario of BH failure on a link in an IABnetwork;

FIG. 20 illustrates an example of several descendant/child IAB nodesdisconnected from IAB-donor;

FIG. 21 is a schematic diagram of an exemplary network architectureillustrating a communication system connected via an intermediatenetwork to a host computer according to the principles in the presentdisclosure;

FIG. 22 is a block diagram of a host computer communicating via anetwork node with a user equipment over an at least partially wirelessconnection according to some embodiments of the present disclosure;

FIG. 23 is a flowchart illustrating exemplary methods implemented in acommunication system including a host computer, a network node and auser equipment for executing a client application at a user equipmentaccording to some embodiments of the present disclosure;

FIG. 24 is a flowchart illustrating exemplary methods implemented in acommunication system including a host computer, a network node and auser equipment for receiving user data at a user equipment according tosome embodiments of the present disclosure;

FIG. 25 is a flowchart illustrating exemplary methods implemented in acommunication system including a host computer, a network node and auser equipment for receiving user data from the user equipment at a hostcomputer according to some embodiments of the present disclosure;

FIG. 26 is a flowchart illustrating exemplary methods implemented in acommunication system including a host computer, a network node and auser equipment for receiving user data at a host computer according tosome embodiments of the present disclosure;

FIG. 27 is a flowchart of an exemplary process in a network nodeaccording to some embodiments of the present disclosure; and

FIG. 28 is a flowchart of an exemplary process in a network node such asa child IAB node according to some embodiments of the present disclosure

FIG. 29 is a flowchart of another exemplary process in a network nodeaccording to some embodiments of the present disclosure;

FIG. 30 is a flowchart of an exemplary process in a network node such asa descendant IAB node according to some embodiments of the presentdisclosure; and

FIG. 31 is a flowchart of an exemplary process in a network node such asa donor IAB node according to some embodiments of the presentdisclosure.

DETAILED DESCRIPTION

This disclosure provides methods and arrangements to allow an IABnetwork to recover faster from link failure as compared with othersolutions by employing an alternative/redundant path of child/descendentIAB node(s) with the IAB-donor node (also referred to as an donor IABnode) to inform the IAB-donor node about link failure, which may thentrigger a topology adaptation procedure to connect the affected IAB node(referred to as the “child IAB node”) to a new parent IAB node, asdescribed herein.

In one or more embodiments, a mechanism for faster link failure recovery(as compared with other solutions) in an IAB (relay) network for variousscenarios is provided, where a backhaul link failure may leave one ormore IAB nodes and UEs disconnected from the IAB-donor, and one or moreof the affected descendant/child IAB nodes have a redundant/alternativeroute to IAB-donor node. One of the descendant IAB nodes (with aredundant/alternative route to IAB-donor node) may be chosen (in casethere are more than one) based on a selection criteria to inform theIAB-donor node about the link failure and assist the IAB-donor node inreestablishing connection with the directly affected IAB node.

Before describing in detail exemplary embodiments, it is noted that theembodiments reside primarily in combinations of apparatus components andprocessing steps related to recovery from a radio link failure in abackhaul network. Accordingly, components have been represented whereappropriate by conventional symbols in the drawings, showing only thosespecific details that are pertinent to understanding the embodiments soas not to obscure the disclosure with details that will be readilyapparent to those of ordinary skill in the art having the benefit of thedescription herein. Like numbers refer to like elements throughout thedescription.

As used herein, relational terms, such as “first” and “second,” “top”and “bottom,” and the like, may be used solely to distinguish one entityor element from another entity or element without necessarily requiringor implying any physical or logical relationship or order between suchentities or elements. The terminology used herein is for the purpose ofdescribing particular embodiments only and is not intended to belimiting of the concepts described herein. As used herein, the singularforms “a”, “an” and “the” are intended to include the plural forms aswell, unless the context clearly indicates otherwise. It will be furtherunderstood that the terms “comprises,” “comprising,” “includes” and/or“including” when used herein, specify the presence of stated features,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof.

In embodiments described herein, the joining term, “in communicationwith” and the like, may be used to indicate electrical or datacommunication, which may be accomplished by physical contact, induction,electromagnetic radiation, radio signaling, infrared signaling oroptical signaling, for example. One having ordinary skill in the artwill appreciate that multiple components may interoperate andmodifications and variations are possible of achieving the electricaland data communication.

In some embodiments described herein, the term “coupled,” “connected,”and the like, may be used herein to indicate a connection, although notnecessarily directly, and may include wired and/or wireless connections.As used herein, the term “topology” refers to the logical arrangement ofthe network referenced to how data and signaling are moved through thenetwork. Thus, modification of the topology discussed herein refers to achange in the logical relationship of the nodes in the network whichmight then impact/change the communication path among the nodes.

The term “network node” is used interchangeably with integrated accessbackhaul (IAB) node and herein can be any kind of network node comprisedin a radio network which may further comprise any of base station (BS),radio base station, base transceiver station (BTS), IAB node, basestation controller (BSC), radio network controller (RNC), g Node B(gNB), evolved Node B (eNB or eNodeB), Node B, multi-standard radio(MSR) radio node such as MSR BS, multi-cell/multicast coordinationentity (MCE), relay node, donor node controlling relay, radio accesspoint (AP), transmission points, transmission nodes, Remote Radio Unit(RRU) Remote Radio Head (RRH), a core network node (e.g., mobilemanagement entity (MME), self-organizing network (SON) node, acoordinating node, positioning node, MDT node, etc.), an external node(e.g., 3rd party node, a node external to the current network), nodes indistributed antenna system (DAS), a spectrum access system (SAS) node,an element management system (EMS), etc. The network node may alsocomprise test equipment. The term “radio node” used herein may be usedto also denote a user equipment (UE), wireless device (WD) such as awireless device (WD) or a radio network node.

In some embodiments, the non-limiting terms wireless device (WD) or auser equipment (UE) are used interchangeably. The UE herein can be anytype of wireless device capable of communicating with a network node oranother UE over radio signals, such as wireless device (WD). The UE mayalso be a radio communication device, target device, device to device(D2D) UE, machine type UE or UE capable of machine to machinecommunication (M2M), low-cost and/or low-complexity UE, a sensorequipped with UE, Tablet, mobile terminals, smart phone, laptop embeddedequipped (LEE), laptop mounted equipment (LME), USB dongles, CustomerPremises Equipment (CPE), an Internet of Things (IoT) device, or aNarrowband IoT (NB-IOT) device etc.

Also, in some embodiments the generic term “radio network node” is used.It can be any kind of a radio network node which may comprise any ofbase station, radio base station, base transceiver station, base stationcontroller, network controller, RNC, evolved Node B (eNB), Node B, gNB,Multi-cell/multicast Coordination Entity (MCE), relay node, accesspoint, radio access point, Remote Radio Unit (RRU) Remote Radio Head(RRH).

An indication generally may explicitly and/or implicitly indicate theinformation it represents and/or indicates. Implicit indication may forexample be based on position and/or resource used for transmission.Explicit indication may for example be based on a parametrization withone or more parameters, and/or one or more index or indices, and/or oneor more bit patterns representing the information. It may in particularbe considered that control signaling as described herein, based on theutilized resource sequence, implicitly indicates the control signalingtype. Transmitting in downlink may pertain to transmission from thenetwork or network node toward the terminal and/or to a descendantnetwork node. Transmitting in uplink may pertain to transmission fromthe terminal toward a donor network node. Uplink and downlink may beconsidered communication directions. In some variants, uplink anddownlink may also be used to described wireless communication betweennetwork nodes, e.g. for wireless backhaul (as described herein) and/orrelay communication and/or (wireless) network communication for examplebetween base stations or similar network nodes, in particularcommunication terminating at such. It may be considered that backhauland/or relay communication and/or network communication is implementedas a form of sidelink or uplink communication or similar thereto.

Note that although terminology from one particular wireless system, suchas, for example, 3GPP LTE and/or New Radio (NR), may be used in thisdisclosure, this should not be seen as limiting the scope of thedisclosure to only the aforementioned system. Other wireless systems,including without limitation Wide Band Code Division Multiple Access(WCDMA), Worldwide Interoperability for Microwave Access (WiMax), UltraMobile Broadband (UMB) and Global System for Mobile Communications(GSM), may also benefit from exploiting the ideas covered within thisdisclosure.

Note further, that functions described herein as being performed by auser equipment or a network node may be distributed over a plurality ofuser equipments and/or network nodes. In other words, it is contemplatedthat the functions of the network node and user equipment describedherein are not limited to performance by a single physical device and,in fact, can be distributed among several physical devices.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms used herein should be interpreted ashaving a meaning that is consistent with their meaning in the context ofthis specification and the relevant art and will not be interpreted inan idealized or overly formal sense unless expressly so defined herein.

Embodiments provide recovery from a radio link failure in a backhaulnetwork.

Referring now to the drawing figures, in which like elements arereferred to by like reference numerals, there is shown in FIG. 21 aschematic diagram of a communication system 10, according to anembodiment, such as a 3GPP-type cellular network that may supportstandards such as LTE and/or NR (5G), which comprises an access network12, such as a radio access network, and a core network 14. The accessnetwork 12 comprises a plurality of network nodes 16 a, 16 b, 16 c, . .. 16 n (referred to collectively as network nodes 16, where only 16 a-16c are illustrated in FIG. 21 ), such as NBs, eNBs, gNBs or other typesof wireless access points, each defining a corresponding coverage area18 a, 18 b . . . 18 n (referred to collectively as coverage areas 18).Each network node 16 a, 16 b, 16 c is connectable to the core network 14over a wired or wireless connection 20. Network nodes 16 may be incommunication with each other via one or more backhaul links and/orbackhaul network. A first user equipment (UE) 22 a located in coveragearea 18 b is configured to wirelessly connect to, or be paged by, thecorresponding network node 16 b. A second UE 22 b in coverage area 18 cis wirelessly connectable to the corresponding network node 16 c. Whilea plurality of UEs 22 a, 22 b (collectively referred to as userequipments 22) are illustrated in this example, the disclosedembodiments are equally applicable to a situation where a sole UE is inthe coverage area or where a sole UE is connecting to the correspondingnetwork node 16. Note that although only two UEs 22 and three networknodes 16 are shown for convenience, the communication system may includemany more UEs 22 and network nodes 16.

Also, it is contemplated that a UE 22 can be in simultaneouscommunication and/or configured to separately communicate with more thanone network node 16 and more than one type of network node 16. Forexample, a UE 22 can have dual connectivity with a network node 16 thatsupports LTE and the same or a different network node 16 that supportsNR. As an example, UE 22 can be in communication with an eNB forLTE/E-UTRAN and a gNB for NR/NG-RAN.

The communication system 10 may itself be connected to a host computer24, which may be embodied in the hardware and/or software of astandalone server, a cloud-implemented server, a distributed server oras processing resources in a server farm. The host computer 24 may beunder the ownership or control of a service provider, or may be operatedby the service provider or on behalf of the service provider. Theconnections 26, 28 between the communication system 10 and the hostcomputer 24 may extend directly from the core network 14 to the hostcomputer 24 or may extend via an optional intermediate network 30. Theintermediate network 30 may be one of, or a combination of more than oneof, a public, private or hosted network. The intermediate network 30, ifany, may be a backbone network or the Internet. In some embodiments, theintermediate network 30 may comprise two or more sub-networks (notshown).

The communication system of FIG. 21 as a whole enables connectivitybetween one of the connected UEs 22 a, 22 b and the host computer 24.The connectivity may be described as an over-the-top (OTT) connection.The host computer 24 and the connected UEs 22 a, 22 b are configured tocommunicate data and/or signaling via the OTT connection, using theaccess network 12, the core network 14, any intermediate network 30 andpossible further infrastructure (not shown) as intermediaries. The OTTconnection may be transparent in the sense that at least some of theparticipating communication devices through which the OTT connectionpasses are unaware of routing of uplink and downlink communications. Forexample, a network node 16 may not or need not be informed about thepast routing of an incoming downlink communication with data originatingfrom a host computer 24 to be forwarded (e.g., handed over) to aconnected UE 22 a. Similarly, the network node 16 need not be aware ofthe future routing of an outgoing uplink communication originating fromthe UE 22 a towards the host computer 24.

A network node 16 is configured to include one or more of an indicationunit 32 and report unit 34 which are configured to perform one or morefunctions described herein. In one or more embodiments, network node 16may optionally include both indication unit 32 and report unit 34 butmay implemented/activate/perform the processes of one unit instead ofthe other unit based on one or more characteristics of a radio linkfailure such as whether the radio link failure is immediately uplink(i.e., communication path toward the donor network node) of the networknode 16 or whether the network node 16 is a descendant network node 16that is affected by the radio link failure.

Example implementations, in accordance with an embodiment, of the UE 22,network node 16 and host computer 24 discussed in the precedingparagraphs will now be described with reference to FIG. 22 . In acommunication system 10, a host computer 24 comprises hardware (HW) 38including a communication interface 40 configured to set up and maintaina wired or wireless connection with an interface of a differentcommunication device of the communication system 10. The host computer24 further comprises processing circuitry 42, which may have storageand/or processing capabilities. The processing circuitry 42 may includea processor 44 and memory 46. In particular, in addition to or insteadof a processor, such as a central processing unit, and memory, theprocessing circuitry 42 may comprise integrated circuitry for processingand/or control, e.g., one or more processors and/or processor coresand/or FPGAs (Field Programmable Gate Array) and/or ASICs (ApplicationSpecific Integrated Circuitry) adapted to execute instructions. Theprocessor 44 may be configured to access (e.g., write to and/or readfrom) memory 46, which may comprise any kind of volatile and/ornonvolatile memory, e.g., cache and/or buffer memory and/or RAM (RandomAccess Memory) and/or ROM (Read-Only Memory) and/or optical memoryand/or EPROM (Erasable Programmable Read-Only Memory).

Processing circuitry 42 may be configured to control any of the methodsand/or processes described herein and/or to cause such methods, and/orprocesses to be performed, e.g., by host computer 24. Processor 44corresponds to one or more processors 44 for performing host computer 24functions described herein. The host computer 24 includes memory 46 thatis configured to store data, programmatic software code and/or otherinformation described herein. In some embodiments, the software 48and/or the host application 50 may include instructions that, whenexecuted by the processor 44 and/or processing circuitry 42, causes theprocessor 44 and/or processing circuitry 42 to perform the processesdescribed herein with respect to host computer 24. The instructions maybe software associated with the host computer 24.

The software 48 may be executable by the processing circuitry 42. Thesoftware 48 includes a host application 50. The host application 50 maybe operable to provide a service to a remote user, such as a UE 22connecting via an OTT connection 52 terminating at the UE 22 and thehost computer 24. In providing the service to the remote user, the hostapplication 50 may provide user data which is transmitted using the OTTconnection 52. The “user data” may be data and information describedherein as implementing the described functionality. In one embodiment,the host computer 24 may be configured for providing control andfunctionality to a service provider and may be operated by the serviceprovider or on behalf of the service provider. The processing circuitry42 of the host computer 24 may enable the host computer 24 to observe,monitor, control, transmit to and/or receive from the network node 16and or the user equipment 22. The processing circuitry 42 of the hostcomputer 24 may include an information unit 54 configured to enable theservice provider to one or more of determine, transmit, receive, forwardand process information related to the indication, RRC signaling and/ormodifying network topology by, for example, the creation of a newbackhaul link.

The communication system 10 further includes a network node 16 providedin a communication system 10 as illustrated in FIG. 22 . Even thoughvarious components have been omitted from network node 16 a, 16 c and 16n in FIG. 22 for ease of understanding, the discussion of the componentsof network node 16, i.e., network node 16 b in FIG. 22 , is equallyapplicable to any of network nodes 16 a and 16 c-16 n where the networknodes 16 may include and use different units depending on thefunctionality of the network node 16 such as whether the network node 16is a donor network node, child network node, parent network node (wherethe parent network node is not shown in FIG. 22 for ease ofunderstanding but may include indication unit 32 and/or report unit 34such as, for example, if the parent network node 16 is a child ordescendant network node to another network node 16), descendant networknode, as described herein. As used herein, the network node directlydownlink from the parent network node is referred to as a child networknode or child IAB node, and the downlink network nodes from the childnetwork node are referred to as descendant network nodes or descendentIAB nodes.

Network node 16 includes hardware 58 enabling it to communicate with thehost computer 24 and with the UE 22. The hardware 58 may include acommunication interface 60 for setting up and maintaining a wired orwireless connection with an interface of a different communicationdevice of the communication system 10, as well as a radio interface 62for setting up and maintaining at least a wireless connection 64 with aUE 22 located in a coverage area 18 served by the network node 16. Theradio interface 62 may be formed as or may include, for example, one ormore RF transmitters, one or more RF receivers, and/or one or more RFtransceivers. The communication interface 60 may be configured tofacilitate a connection 66 to the host computer 24. The connection 66may be direct or it may pass through a core network 14 of thecommunication system 10 and/or through one or more intermediate networks30 outside the communication system 10.

In the embodiment shown, the hardware 58 of the network node 16 furtherincludes processing circuitry 68. The processing circuitry 68 mayinclude a processor 70 and a memory 72. In particular, in addition to orinstead of a processor, such as a central processing unit, and memory,the processing circuitry 68 may comprise integrated circuitry forprocessing and/or control, e.g., one or more processors and/or processorcores and/or FPGAs (Field Programmable Gate Array) and/or ASICs(Application Specific Integrated Circuitry) adapted to executeinstructions. The processor 70 may be configured to access (e.g., writeto and/or read from) the memory 72, which may comprise any kind ofvolatile and/or nonvolatile memory, e.g., cache and/or buffer memoryand/or RAM (Random Access Memory) and/or ROM (Read-Only Memory) and/oroptical memory and/or EPROM (Erasable Programmable Read-Only Memory).

Thus, the network node 16 further has software 74 stored internally in,for example, memory 72, or stored in external memory (e.g., database,storage array, network storage device, etc.) accessible by the networknode 16 via an external connection. The software 74 may be executable bythe processing circuitry 68. The processing circuitry 68 may beconfigured to control any of the methods and/or processes describedherein and/or to cause such methods, and/or processes to be performed,e.g., by network node 16. Processor 70 corresponds to one or moreprocessors 70 for performing network node 16 functions described herein.The memory 72 is configured to store data, programmatic software codeand/or other information described herein. In some embodiments, thesoftware 74 may include instructions that, when executed by theprocessor 70 and/or processing circuitry 68, causes the processor 70and/or processing circuitry 68 to perform the processes described hereinwith respect to network node 16. For example, processing circuitry 68 ofthe network node 16 may include indication unit 32 configured to performone or more radio link failure recovery functions as may be performed bya descendant network node 16 c, as described herein. In another example,processing circuitry 68 of the network node 16 may include report unit34 configured to perform one or more radio link failure recoveryfunctions as may be performed by child network node 16 b, as describedherein. In another example, processing circuitry 68 of the network node16 may include topology unit 35 configured to perform one or more radiolink failure recovery functions as may be performed by donor networknode 16 a, as described herein.

The communication system 10 further includes the UE 22 already referredto. The UE 22 may have hardware 80 that may include a radio interface 82configured to set up and maintain a wireless connection 64 with anetwork node 16 serving a coverage area 18 in which the UE 22 iscurrently located. The radio interface 82 may be formed as or mayinclude, for example, one or more RF transmitters, one or more RFreceivers, and/or one or more RF transceivers.

The hardware 80 of the UE 22 further includes processing circuitry 84.The processing circuitry 84 may include a processor 86 and memory 88. Inparticular, in addition to or instead of a processor, such as a centralprocessing unit, and memory, the processing circuitry 84 may compriseintegrated circuitry for processing and/or control, e.g., one or moreprocessors and/or processor cores and/or FPGAs (Field Programmable GateArray) and/or ASICs (Application Specific Integrated Circuitry) adaptedto execute instructions. The processor 86 may be configured to access(e.g., write to and/or read from) memory 88, which may comprise any kindof volatile and/or nonvolatile memory, e.g., cache and/or buffer memoryand/or RAM (Random Access Memory) and/or ROM (Read-Only Memory) and/oroptical memory and/or EPROM (Erasable Programmable Read-Only Memory).

Thus, the UE 22 may further comprise software 90, which is stored in,for example, memory 88 at the UE 22, or stored in external memory (e.g.,database, storage array, network storage device, etc.) accessible by theUE 22. The software 90 may be executable by the processing circuitry 84.The software 90 may include a client application 92. The clientapplication 92 may be operable to provide a service to a human ornon-human user via the UE 22, with the support of the host computer 24.In the host computer 24, an executing host application 50 maycommunicate with the executing client application 92 via the OTTconnection 52 terminating at the UE 22 and the host computer 24. Inproviding the service to the user, the client application 92 may receiverequest data from the host application 50 and provide user data inresponse to the request data. The OTT connection 52 may transfer boththe request data and the user data. The client application 92 mayinteract with the user to generate the user data that it provides.

The processing circuitry 84 may be configured to control any of themethods and/or processes described herein and/or to cause such methods,and/or processes to be performed, e.g., by UE 22. The processor 86corresponds to one or more processors 86 for performing UE 22 functionsdescribed herein. The UE 22 includes memory 88 that is configured tostore data, programmatic software code and/or other informationdescribed herein. In some embodiments, the software 90 and/or the clientapplication 92 may include instructions that, when executed by theprocessor 86 and/or processing circuitry 84, causes the processor 86and/or processing circuitry 84 to perform the processes described hereinwith respect to UE 22.

In some embodiments, the inner workings of the network node 16, UE 22,and host computer 24 may be as shown in FIG. 22 and independently, thesurrounding network topology may be that of FIG. 21 .

In FIG. 22 , the OTT connection 52 has been drawn abstractly toillustrate the communication between the host computer 24 and the userequipment 22 via the network node 16, without explicit reference to anyintermediary devices and the precise routing of messages via thesedevices. Network infrastructure may determine the routing, which it maybe configured to hide from the UE 22 or from the service provideroperating the host computer 24, or both. While the OTT connection 52 isactive, the network infrastructure may further take decisions by whichit dynamically changes the routing (e.g., on the basis of load balancingconsideration or reconfiguration of the network).

The wireless connection 64 between the UE 22 and the network node 16 isin accordance with the teachings of the embodiments described throughoutthis disclosure. One or more of the various embodiments improve theperformance of OTT services provided to the UE 22 using the OTTconnection 52, in which the wireless connection 64 may form the lastsegment. More precisely, the teachings of some of these embodiments mayimprove the data rate, latency, and/or power consumption and therebyprovide benefits such as reduced user waiting time, relaxed restrictionon file size, better responsiveness, extended battery lifetime, etc. Insome embodiments, a measurement procedure may be provided for thepurpose of monitoring data rate, latency and other factors on which theone or more embodiments improve. There may further be an optionalnetwork functionality for reconfiguring the OTT connection 52 betweenthe host computer 24 and UE 22, in response to variations in themeasurement results. The measurement procedure and/or the networkfunctionality for reconfiguring the OTT connection 52 may be implementedin the software 48 of the host computer 24 or in the software 90 of theUE 22, or both. In embodiments, sensors (not shown) may be deployed inor in association with communication devices through which the OTTconnection 52 passes; the sensors may participate in the measurementprocedure by supplying values of the monitored quantities exemplifiedabove, or supplying values of other physical quantities from whichsoftware 48, 90 may compute or estimate the monitored quantities. Thereconfiguring of the OTT connection 52 may include message format,retransmission settings, preferred routing etc.; the reconfiguring neednot affect the network node 16, and it may be unknown or imperceptibleto the network node 16. Some such procedures and functionalities may beknown and practiced in the art. In certain embodiments, measurements mayinvolve proprietary UE signaling facilitating the host computer's 24measurements of throughput, propagation times, latency and the like. Insome embodiments, the measurements may be implemented in that thesoftware 48, 90 causes messages to be transmitted, in particular emptyor ‘dummy’ messages, using the OTT connection 52 while it monitorspropagation times, errors etc.

Thus, in some embodiments, the host computer 24 includes processingcircuitry 42 configured to provide user data and a communicationinterface 40 that is configured to forward the user data to a cellularnetwork for transmission to the UE 22. In some embodiments, the cellularnetwork also includes the network node 16 with a radio interface 62. Insome embodiments, the network node 16 is configured to, and/or thenetwork node's 16 processing circuitry 68 is configured to perform thefunctions and/or methods described herein forpreparing/initiating/maintaining/supporting/ending a transmission to theUE 22, and/or preparing/terminating/maintaining/supporting/ending inreceipt of a transmission from the UE 22.

In some embodiments, the host computer 24 includes processing circuitry42 and a communication interface 40 that is configured to acommunication interface 40 configured to receive user data originatingfrom a transmission from a UE 22 to a network node 16. In someembodiments, the UE 22 is configured to, and/or comprises a radiointerface 82 and/or processing circuitry 84 configured to perform thefunctions and/or methods described herein forpreparing/initiating/maintaining/supporting/ending a transmission to thenetwork node 16, and/orpreparing/terminating/maintaining/supporting/ending in receipt of atransmission from the network node 16.

Although FIGS. 21 and 22 show various “units” such as indication unit32, and report unit 34 as being within a respective processor, it iscontemplated that these units may be implemented such that a portion ofthe unit is stored in a corresponding memory within the processingcircuitry. In other words, the units may be implemented in hardware orin a combination of hardware and software within the processingcircuitry.

FIG. 23 is a flowchart illustrating an exemplary method implemented in acommunication system, such as, for example, the communication system ofFIGS. 21 and 22 , in accordance with one embodiment. The communicationsystem may include a host computer 24, a network node 16 and a UE 22,which may be those described with reference to FIG. 22 . In a first stepof the method, the host computer 24 provides user data (Block S100). Inan optional substep of the first step, the host computer 24 provides theuser data by executing a host application, such as, for example, thehost application 50 (Block S102). In a second step, the host computer 24initiates a transmission carrying the user data to the UE 22 (BlockS104). In an optional third step, the network node 16 transmits to theUE 22 the user data which was carried in the transmission that the hostcomputer 24 initiated, in accordance with the teachings of theembodiments described throughout this disclosure (Block S106). In anoptional fourth step, the UE 22 executes a client application, such as,for example, the client application 92, associated with the hostapplication 50 executed by the host computer 24 (Block S108).

FIG. 24 is a flowchart illustrating an exemplary method implemented in acommunication system, such as, for example, the communication system ofFIG. 21 , in accordance with one embodiment. The communication systemmay include a host computer 24, a network node 16 and a UE 22, which maybe those described with reference to FIGS. 21 and 22 . In a first stepof the method, the host computer 24 provides user data (Block S110). Inan optional substep (not shown) the host computer 24 provides the userdata by executing a host application, such as, for example, the hostapplication 50. In a second step, the host computer 24 initiates atransmission carrying the user data to the UE 22 (Block S112). Thetransmission may pass via the network node 16, in accordance with theteachings of the embodiments described throughout this disclosure. In anoptional third step, the UE 22 receives the user data carried in thetransmission (Block S114).

FIG. 25 is a flowchart illustrating an exemplary method implemented in acommunication system, such as, for example, the communication system ofFIG. 21 , in accordance with one embodiment. The communication systemmay include a host computer 24, a network node 16 and a UE 22, which maybe those described with reference to FIGS. 21 and 22 . In an optionalfirst step of the method, the UE 22 receives input data provided by thehost computer 24 (Block S116). In an optional substep of the first step,the UE 22 executes the client application 92, which provides the userdata in reaction to the received input data provided by the hostcomputer 24 (Block S118). Additionally or alternatively, in an optionalsecond step, the UE 22 provides user data (Block S120). In an optionalsubstep of the second step, the UE provides the user data by executing aclient application, such as, for example, client application 92 (BlockS122). In providing the user data, the executed client application 92may further consider user input received from the user. Regardless ofthe specific manner in which the user data was provided, the UE 22 mayinitiate, in an optional third substep, transmission of the user data tothe host computer 24 (Block S124). In a fourth step of the method, thehost computer 24 receives the user data transmitted from the UE 22, inaccordance with the teachings of the embodiments described throughoutthis disclosure (Block S126).

FIG. 26 is a flowchart illustrating an exemplary method implemented in acommunication system, such as, for example, the communication system ofFIG. 21 , in accordance with one embodiment. The communication systemmay include a host computer 24, a network node 16 and a UE 22, which maybe those described with reference to FIGS. 21 and 22 . In an optionalfirst step of the method, in accordance with the teachings of theembodiments described throughout this disclosure, the network node 16receives user data from the UE 22 (Block S128). In an optional secondstep, the network node 16 initiates transmission of the received userdata to the host computer 24 (Block S130). In a third step, the hostcomputer 24 receives the user data carried in the transmission initiatedby the network node 16 (Block S132).

FIG. 27 is a flowchart of an exemplary process in a network node 16 suchas a child network node 16 b (i.e., child IAB node 16 b) that is incommunication with descendant network node(s) 16 c-16 n (i.e.,descendent IAB node 16 c-16 n) according to some embodiments of thepresent disclosure. One or more Blocks and/or functions performed bynetwork node 16 may be performed by one or more elements of network node16 such as by indication unit 32 in processing circuitry 68, processor70, communication interface 60, radio interface 62, etc. In one or moreembodiments, network node 16 such as via one or more of processingcircuitry 68, processor 70, radio interface 62 and communicationinterface 60 is configured to transmit (Block S134) an indication to asubset of the plurality of descendant network nodes 16 c-16 n inresponse to a radio link failure where the indication configured totrigger each descendant network node 16 c to modify data transmission.In one or more embodiments, a descendant network node 16 c may refer toone or more network nodes 16 that are on a downlink path from thenetwork node 16 to the UE 22. In one or more embodiments, network node16 such as via one or more of processing circuitry 68, processor 70,radio interface 62 and communication interface 60 is configured toreceive (Block S136) radio resource control, RRC, signaling from one ofthe subset of the plurality of descendant network nodes 16 c-16 n. Inone or more embodiments, network node 16 such as via one or more ofprocessing circuitry 68, processor 70, radio interface 62 andcommunication interface 60 is configured to transmit (Block S138) modifynetwork topology based at least in part on the RRC signaling.

According to one or more embodiments, the modifying of data transmissionincludes causing at least a reduction in one of a Packet DataConvergence Protocol, PDCP, Radio Link Control, RLC, and Medium AccessControl, MAC, process. According to one or more embodiments, theindication includes a report that includes at least one of: anindication of a reason for radio link failure and measurement reports.

FIG. 28 is a flowchart of an exemplary process in a network node 16 suchas a child network node 16 b with descendant IAB node(s) 16 c-16 naccording to some embodiments of the present disclosure. One or moreBlocks and/or functions performed by network node 16 may be performed byone or more elements of network node 16 such as by indication unit 32 inprocessing circuitry 68, processor 70, communication interface 60, radiointerface 62, etc. In one or more embodiments, network node 16 such asvia one or more of processing circuitry 68, processor 70, radiointerface 62 and communication interface 60 is configured to detect(Block S140) a backhaul link failure between the child IAB node 16 b andthe first parent IAB node 16, as described herein.

In one or more embodiments, network node 16 such as via one or more ofprocessing circuitry 68, processor 70, radio interface 62 andcommunication interface 60 is configured to in response to the detectedbackhaul link failure, cause (Block S142) transmission of a radio linkfailure indication to the descendant IAB node 16 c, as described herein.In one or more embodiments, network node 16 such as via one or more ofprocessing circuitry 68, processor 70, radio interface 62 andcommunication interface 60 is configured to receive (Block S144)signaling indicating for the child IAB node 16 b to connect to a secondparent IAB node, as described herein. In one or more embodiments,network node 16 such as via one or more of processing circuitry 68,processor 70, radio interface 62 and communication interface 60 isconfigured to modify (Block S146) network topology at least in part byconnecting to the second parent IAB node 16, as described herein.

According to one or more embodiments, the radio link failure indicationis configured to cause each descendant IAB node 16 c receiving the radiolink failure indication to modify data transmission and remain on anestablished communication path to the child IAB node 16 b where themodifying of data transmission includes one of: at least temporarilypausing data transmission, and at least temporarily reducing a datatransmission rate. According to one or more embodiments, the radio linkfailure indication is configured to cause each descendant IAB node 16 creceiving the radio link failure indication to modify data transmissionand remain on an established communication path to the child IAB node 16b where the modifying of data transmission includes limiting at leastone of a packet data convergence protocol, PDCP, process, radio linkcontrol, RLC, process and medium access control, MAC, process. Accordingto one or more embodiments, the transmission of the radio link failureindication to the descendant IAB node 16 c includes one of broadcastingthe radio link failure indication to the descendant IAB node 16 c andtransmitting the radio link failure indication to the descendant IABnode 16 c via dedicated signaling.

According to one or more embodiments, the radio link failure indicationis configured to cause each descendant IAB node 16 c receiving the radiolink failure indication to modify data transmission and remain on anestablished communication path to the child IAB node 16 b. According toone or more embodiments, the radio link failure indication is a failurereport that indicates at least one of: a cause of the detected backhaullink failure; IAB node identification; failure report identifier;backhaul link failure time; and results of measurements performed by thechild IAB node 16 b. According to one or more embodiments, the radiolink failure indication is a failure report that includes results ofmeasurements performed by the child IAB node 16 b where the results ofthe measurements indicating at least one discoverable parent IAB node16. According to one or more embodiments, the signaling is RRC signalingthat is received from the descendant IAB node 16 c where the RRCsignaling includes an RRC reconfiguration message.

FIG. 29 is a flowchart of another exemplary process in a network node 16such as a descendant network node 16 c according to some embodiments ofthe present disclosure. One or more Blocks and/or functions performed bynetwork node 16 may be performed by one or more elements of network node16 such as by report unit 34 in processing circuitry 68, processor 70,communication interface 60, radio interface 62, etc. In one or moreembodiments, descendant network node 16 c such as via one or more ofprocessing circuitry 68, processor 70, radio interface 62 andcommunication interface 60 is configured to receive (Block S146), fromthe second network node 16 (e.g., a child IAB node 16 b with descendantIAB nodes 16 c-16 n), an indication associated with a radio linkfailure.

In one or more embodiments, the descendant network node 16 c such as viaone or more of processing circuitry 68, processor 70, radio interface 62and communication interface 60 is configured to modify (Block S148) datatransmission in response to the indication. In one or more embodiments,the descendant network node 16 c such as via one or more of processingcircuitry 68, processor 70, radio interface 62 and communicationinterface 60 is configured to transmit (Block S150) a report associatedwith the indication. In one or more embodiments, the descendant networknode 16 c such as via one or more of processing circuitry 68, processor70, radio interface 62 and communication interface 60 is configured toreceive (Block S152) radio resource control, RRC, signaling associatedwith the report. In one or more embodiments, the descendant network node16 c such as via one or more of processing circuitry 68, processor 70,radio interface 62 and communication interface 60 is configured totransmit (Block S154) the RRC signaling toward the second network node16 (e.g., child IAB node 16 b) where the RRC signaling configured tocause the second network node 16 to modify network topology.

According to one or more embodiments, the report is transmitted on analternative path to a control node, i.e., donor IAB node 16 a, thatbypasses the second network node 16. According to one or moreembodiments, the modifying of data transmission includes causing atleast a reduction in one of a Packet Data Convergence Protocol, PDCP,Radio Link Control, RLC, and Medium Access Control, MAC, process.According to one or more embodiments, the indication includes the reportthat includes at least one of: an indication of a reason for radio linkfailure and measurement reports.

FIG. 30 is a flowchart of another exemplary process in a network node 16such as a descendant network node 16 c, i.e., descendant IAB node 16 c,according to some embodiments of the present disclosure. One or moreBlocks and/or functions performed by descendant network node 16 may beperformed by one or more elements of network node 16 such as by reportunit 34 in processing circuitry 68, processor 70, communicationinterface 60, radio interface 62, etc. In one or more embodiments,descendant network node 16 such as via one or more of processingcircuitry 68, processor 70, radio interface 62 and communicationinterface 60 is configured to receive (Block S156) a radio link failureindication, as described herein. In one or more embodiments, descendantnetwork node 16 c such as via one or more of processing circuitry 68,processor 70, radio interface 62 and communication interface 60 isconfigured to in response to the radio link failure indication (BlockS158), modify data transmission and remain on an establishedcommunication path to the child IAB node 16 b, and transmit the radiolink failure indication to the donor node 16 a.

In one or more embodiments, descendant network node 16 c such as via oneor more of processing circuitry 68, processor 70, radio interface 62 andcommunication interface 60 is configured to receive (Block S160)signaling from the donor IAB node 16 a where the signaling indicates forthe child IAB node 16 b to modify network topology at least in part byconnecting to a second parent IAB node 16, as described herein. In oneor more embodiments, descendant network node 16 c such as via one ormore of processing circuitry 68, processor 70, radio interface 62 andcommunication interface 60 is configured to cause (Block S162)transmission of the signaling to the child IAB node 16 b, as describedherein.

According to one or more embodiments, the processing circuitry 68 isfurther configured to: determine whether an alternate communication pathfrom the descendant IAB node 16 c to the donor IAB node 16 a isconfigured; and if the alternate communication path is configured, causetransmission of the radio link failure indication along the alternativecommunication path to the donor IAB node 16 a. According to one or moreembodiments, the processing circuitry 68 is further configured to:determine whether an alternate communication path from the descendantIAB node 16 c to the donor IAB node 16 a is configured; and if thealternate communication path is not configured, cause transmission ofthe radio link failure indication to another descendant IAB node 16 c.According to one or more embodiments, the modifying of data transmissionincludes one of: at least temporarily pausing data transmission; and atleast temporarily reducing a data transmission rate.

According to one or more embodiments, the modifying of data transmissionincludes limiting at least one of a packet data convergence protocol,PDCP, process, radio link control, RLC, process and medium accesscontrol, MAC, process.

According to one or more embodiments, the radio link failure indicationis a failure report destined for a donor IAB node 16 a where the failurereport indicates at least one of: a cause of the radio link failure; IABnode identification; failure report identifier; backhaul link failuretime; and results of measurements performed by the child IAB node 16 b.According to one or more embodiments, the radio link failure indicationis a failure report destined for a donor IAB node 16 a where the failurereport includes results of measurements performed by the child IAB node16 b and where the results of the measurements indicating at least onediscoverable parent IAB node 16. According to one or more embodiments,the signaling is RRC signaling that includes an RRC reconfigurationmessage. According to one or more embodiments, the descendant IAB node16 c is one of: a logically next hop from the first parent IAB node 16;and at least two logical next hops from the first parent IAB node 16.

FIG. 31 is a flowchart of another exemplary process in a network node 16such as a donor network node 16 a, i.e., donor IAB node 16 a, accordingto some embodiments of the present disclosure. One or more Blocks and/orfunctions performed by donor network node 16 a may be performed by oneor more elements of network node 16 such as by topology unit 35 inprocessing circuitry 68, processor 70, communication interface 60, radiointerface 62, etc. In one or more embodiments, donor network node 16 asuch as via one or more of processing circuitry 68, processor 70, radiointerface 62 and communication interface 60 is configured to receive(block S164) a radio link failure indication from one of the at leastone descendent IAB nodes 16 c where the radio link failure indicationindicates a radio link failure between the child IAB node 16 b and thefirst parent IAB node 16, as described herein.

In one or more embodiments, donor network node 16 a such as via one ormore of processing circuitry 68, processor 70, radio interface 62 andcommunication interface 60 is configured to determine (Block S166) asecond parent IAB node 16 for the child IAB node 16 b to connect tobased at least in part on the radio link failure indication, asdescribed herein. In one or more embodiments, donor network node 16 asuch as via one or more of processing circuitry 68, processor 70, radiointerface 62 and communication interface 60 is configured to cause(Block S168) transmission of signaling to the child IAB node 16 b wherethe signaling indicates for the child IAB node 16 b to modify a networktopology at least in part by connecting to the second parent IAB node16, as described herein.

According to one or more embodiments, the radio link failure indicationis configured to cause each descendant IAB node 16 c receiving the radiolink failure indication to modify data transmission and remain on anestablished communication path to the child IAB node 16 b where themodifying of data transmission includes one of: at least temporarilypausing data transmission, and at least temporarily reducing a datatransmission rate. According to one or more embodiments, the radio linkfailure indication is configured to cause each descendant IAB node 16 creceiving the radio link failure indication to modify data transmissionand remain on an established communication path to the child IAB node 16b where the modifying of data transmission includes limiting at leastone of a packet data convergence protocol, PDCP, process, radio linkcontrol, RLC, process and medium access control, MAC, process. Accordingto one or more embodiments, the radio link failure indication isconfigured to cause each descendant IAB node 16 c receiving the radiolink failure indication to modify data transmission and remain on anestablished communication path to the descendant IAB node 16 c.

According to one or more embodiments, the indication is a failure reportdestined for a donor IAB node 16 a, the failure report indicates atleast one of: a cause of the radio link failure; IAB nodeidentification; failure report identifier; backhaul link failure time;and results of measurements performed by the child IAB node 16 b.According to one or more embodiments, the radio link failure indicationis a failure report including results of measurements performed by thechild IAB node 16 b where the results of the measurements indicates atleast one discoverable parent IAB node 16. According to one or moreembodiments, the signaling is RRC signaling that includes an RRCreconfiguration message. According to one or more embodiments, the atleast one descendant IAB node 16 c is a plurality of descendant IABnodes 16 c-16 n.

Embodiments provide for recovery from a radio link failure in a backhaulnetwork. In particular, having generally described arrangements forrecovery from a radio link failure in a backhaul network, details forthese arrangements, functions and processes are provided as follows, andwhich may be implemented by the network node/IAB node 16 and/or hostcomputer 24.

When an IAB node 16 (referred to as “child IAB node 16 b” in one or moreembodiments) detects a type of link failure towards its parent IAB node16, e.g., radio link failure, on its backhaul link, the IAB node 16 maysend a first indication (referred to as primary indication(s) in one ormore embodiments and/or examples) to other descendant IAB nodes 16 c-16n/UEs 22 informing about such a failure. This can be done in a dedicatedmanner (i.e., one by one to each child/descendant IAB node 16 c via aMAC CE, PDCP control PDU, etc.) or broadcast (e.g., in a SIB, systeminformation block).

These primary indications may result in that the transmissions of thedescendant IAB nodes 16 and/or UEs 22 that receive such an indicationmay need to be modified. For example, the transmissions may be at lasttemporarily halted, or the transmission rate of Downlink (DL)/Uplink(UL) data may be at least temporarily reduced. In other words, receivingsuch an indication may result in some of the PDCP, RLC, and MACprocesses are halted or limited or reduced. In one or more embodiments,the transmissions of descendant IAB nodes 16 and/or UEs 22 in theestablished communication path toward child IAB node 16 b are modifiedwhile the transmissions of other descendant IAB nodes 16 and/or UEs 22on a different communication that still has connectivity to donor IABnode 16 a may not modify their transmissions based on the primaryindications. Further, in one or more embodiments, one or more of theother descendant IAB nodes 16 may still receive the primary indicationsfor forwarding and/or transmission of the primary indications to thedonor IAB node 16 a.

The primary indication can include a failure report that is to beforwarded to the donor CU of an IAB node 16, i.e., IAB donor node 16 a.One possible purpose of the primary indication is for the descendant IABnodes 16 c-16 n to pause/reduce transmission toward the child IAB node16 b and possibly to find alternate parents IAB node 16 fortransmitting, for example, a failure report. While the final destinationof the failure reports is the donor CU, the message may help the CUchoose/select the new parent IAB node 16 to the child IAB node 16 b. Asused herein, a descendant IAB node 16 c may correspond to a child IABnode 16 b that is more than two logical hops from the parent IAB node16. The failure report can also be sent instead in a separate messageafter the primary indication (e.g., a secondary indication). The childIAB node 16 b can decide to send the failure report only to itsdescendant IAB nodes 16 c-16 n which already have alternate paths if thechild IAB node 16 b has such information available.

The failure report can contain information such as one or more of thefollowing:

-   -   the cause for the link failure,    -   IAB node 16 identification,    -   failure report ID,    -   failure time,    -   latest measurement results from the child IAB node 16 b,    -   among other data.

The measurement report can include the latest measurement that the childIAB node 16 b has before failure, and/or can include a measurementperformed after failure (e.g., based on a measurement configuration thatwas received from the CU that becomes active only when backhaul failureis detected). The measurement results may contain a list of cells thatthe child IAB node 16 b has discovered as possible parent IAB nodes 16(which may have been defined by some threshold signal quality valuespecified by measurement configuration) and may be ordered in the listaccording to the quality (e.g., in descending order of signal strength).Note that the cells of a descendant IAB node 16 c of the child IAB node16 b could be part of the measurement result.

If a descendant IAB node 16 c has an alternate path to the donor IABnode 16 a, the descendant IAB node 16 c forwards that information (e.g.,measurement report) towards the CU via that path. This can be via a newmessage (e.g., new F1 message, new RRC message) or it can be included inan enhanced version of existing messages (e.g., F1 UL RRC transfermessage, RRC Measurement report, etc.). The identification of the childIAB node 16 b can be a piece of information that is added whenconstructing the F1 or RRC message used to send the failure report,rather than including such information within the failure report itself.The identity of the descendant IAB node 16 c can also be included in theF1 or RRC message in order to cause the CU to later send a response tothat message. The descendant IAB node 16 c can send a message to thechild IAB node 16 b indicating that it has sent the failure report asinstructed. The child IAB node 16 b, upon receiving this indication, cansend another message to other descendant IAB nodes 16 c-16 n that thefailure report has been sent, thereby informing the other descendant IABnodes 16 c-16 n to stop the forwarding of the failure report on itsbehalf, if they have not done so already.

If a descendant IAB node 16 c has no alternate path to the donor networknode 16 a, i.e., IAB donor node 16 a, then the descendant IAB node 16 ccan pass the report to its descendant IAB node 16 c and the process isrepeated hierarchically.

When the CU receives the failure report, it may identify the affectedchild IAB node 16 b by looking into IAB node 16 identification, and theadditional information contained within the failure report (i.e.,measurement result) in order to determine the best alternate parent forthe child IAB node 16 b.

The CU then prepares an RRC Reconfiguration message to the child IABnode 16 b, which contains the configuration that the child IAB node 16 bmay use to connect to the new target parent IAB node 16. Since the CUknows the descendant IAB node 16 c that forwarded the message (eitherimplicitly or by looking into the descendant IAB node 16 cidentification info in the header of the F1/RRC message that deliveredthe failure report), the CU may be able to deduce the path on which tosend the message. This may occur by putting the indicated descendant IABnode 16 c address in the outgoing container message (if the descendantIAB node 16 c has different L2 addresses for each alternate path to thedonor, for example). The RRC reconfiguration message is then sent to thechild IAB node 16 b via the descendant IAB node 16 c (for example, thereconfiguration message is embedded in an outer message destined to thedescendant IAB node 16 c).

The descendant IAB node 16 c, upon getting this RRC reconfigurationmessage, extracts the RRC reconfiguration message destined for the childIAB node 16 and forwards it to the child IAB node 16. The child IAB node16 b applies the RRC reconfiguration and connects to the target parentIAB node 16 indicated in the reconfiguration message. The child IAB node16 b can send another indication to its descendant IAB nodes 16 c-16 nindicating that the backhaul connection has been restored, therebytriggering the descendant IAB nodes 16 c-16 n to resume normal operation(e.g., resuming sending UL data). In other words, the descendant IABnodes 16 c-16 n may remain on the established communication path to thechild IAB node 16 b while the process for modifying the network topologyis performed, thereby at least temporarily preventing each descendantIAB node 16 c from initiating backup link discovery procedures toconnect to an alternate communication path to donor IAB node 16 a.

EXAMPLES

It is noted that the “network node 16” referred to below may be IAB node16 such as a descendant IAB node 16, child IAB node 16, etc.

Example A1. A network node 16 configured to communicate with a pluralityof descendant network nodes 16 c-16 n over a backhaul network, thenetwork node 16 configured to, and/or comprising a radio interface 62and/or comprising processing circuitry 68 configured to:

transmit an indication to a subset of the plurality of descendantnetwork nodes 16 c-16 n in response to a radio link failure, theindication configured to trigger each descendant network node 16 c tomodify data transmission;

receive radio resource control, RRC, signaling from one of the subset ofthe plurality of descendant network nodes 16 c-16 n; and

modify network topology based at least in part on the RRC signaling.

Example A2. The network node 16 of Example A1, wherein modifying datatransmission includes causing at least a reduction in one of a PacketData Convergence Protocol, PDCP, Radio Link Control, RLC, and MediumAccess Control, MAC, process.

Example A3. The network node 16 of Example A1, wherein the indicationincludes a report that includes at least one of:

an indication of a reason for radio link failure; and

measurement reports.

Example B1. A method implemented in a network node 16 configured tocommunicate with a plurality of descendant network nodes 16 c-16 n overa backhaul network, the method comprising:

transmitting an indication to a subset of the plurality of descendantnetwork nodes 16 c-16 n in response to a radio link failure, theindication configured to trigger each descendant network node 16 c tomodify data transmission;

receiving radio resource control, RRC, signaling from one of the subsetof the plurality of descendant network nodes 16 c-16 n; and

modifying network topology based at least in part on the RRC signaling.

Example B2. The method of Example B1, wherein modifying datatransmission includes causing at least a reduction in one of a PacketData Convergence Protocol, PDCP, Radio Link Control, RLC, and MediumAccess Control, MAC, process.

Example B3. The method of Example B1, wherein the indication includes areport that includes at least one of:

an indication of a reason for radio link failure; and

measurement reports.

Example C1. A first network node 16 configured to communicate with asecond network node 16 over a backhaul network, the first network node16 configured to, and/or comprising a radio interface 62 and/orprocessing circuitry 68 configured to:

-   -   receive, from the second network node 16, an indication        associated with a radio link failure;    -   modify data transmission in response to the indication;    -   transmit a report associated with the indication;    -   receive radio resource control, RRC, signaling associated with        the report; and    -   transmit the RRC signaling toward the second network node, the        RRC signaling configured to cause the second node to modify        network topology.

Example C2. The first network node 16 of Example C1, wherein the reportis transmitted on an alternative path to a control network node thatbypasses the second network node 16.

Example C3. The first network node 16 of Example C1, wherein modifyingdata transmission includes causing at least a reduction in one of aPacket Data Convergence Protocol, PDCP, Radio Link Control, RLC, andMedium Access Control, MAC, process.

Example C4. The first network node 16 of Example C1, wherein theindication includes the report that includes at least one of:

an indication of a reason for radio link failure; and

measurement reports.

Example D1. A method implemented in a first network node 16 that isconfigured to communicate with a second network node 16 over a backhaulnetwork, the method comprising:

-   -   receiving, from the second network node 16, an indication        associated with a radio link failure;    -   modifying data transmission in response to the indication;    -   transmitting a report associated with the indication;    -   receiving radio resource control, RRC, signaling associated with        the report; and    -   transmitting the RRC signaling toward the second network node        16, the RRC signaling configured to cause the second network        node 16 to modify network topology.

Example D2. The method of Example D1, wherein the report is transmittedon an alternative path to a control network node 16 that bypasses thesecond network node 16.

Example D3. The method of Example D1, wherein modifying datatransmission includes causing at least a reduction in one of a PacketData Convergence Protocol, PDCP, Radio Link Control, RLC, and MediumAccess Control, MAC, process

Example D4. The method of Example D1, wherein the indication includesthe report that includes at least one of:

an indication of a reason for radio link failure; and

measurement reports.

As will be appreciated by one of skill in the art, the conceptsdescribed herein may be embodied as a method, data processing system,computer program product and/or computer storage media storing anexecutable computer program. Accordingly, the concepts described hereinmay take the form of an entirely hardware embodiment, an entirelysoftware embodiment or an embodiment combining software and hardwareaspects all generally referred to herein as a “circuit” or “module.” Anyprocess, step, action and/or functionality described herein may beperformed by, and/or associated to, a corresponding module, which may beimplemented in software and/or firmware and/or hardware. Furthermore,the disclosure may take the form of a computer program product on atangible computer usable storage medium having computer program codeembodied in the medium that can be executed by a computer. Any suitabletangible computer readable medium may be utilized including hard disks,CD-ROMs, electronic storage devices, optical storage devices, ormagnetic storage devices.

Some embodiments are described herein with reference to flowchartillustrations and/or block diagrams of methods, systems and computerprogram products. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer (to therebycreate a special purpose computer), special purpose computer, or otherprogrammable data processing apparatus to produce a machine, such thatthe instructions, which execute via the processor of the computer orother programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

These computer program instructions may also be stored in a computerreadable memory or storage medium that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer readablememory produce an article of manufacture including instruction meanswhich implement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer orother programmable data processing apparatus to cause a series ofoperational steps to be performed on the computer or other programmableapparatus to produce a computer implemented process such that theinstructions which execute on the computer or other programmableapparatus provide steps for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

It is to be understood that the functions/acts noted in the blocks mayoccur out of the order noted in the operational illustrations. Forexample, two blocks shown in succession may in fact be executedsubstantially concurrently or the blocks may sometimes be executed inthe reverse order, depending upon the functionality/acts involved.Although some of the diagrams include arrows on communication paths toshow a primary direction of communication, it is to be understood thatcommunication may occur in the opposite direction to the depictedarrows.

Computer program code for carrying out operations of the conceptsdescribed herein may be written in an object oriented programminglanguage such as Java® or C++. However, the computer program code forcarrying out operations of the disclosure may also be written inconventional procedural programming languages, such as the “C”programming language. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer. In the latter scenario, theremote computer may be connected to the user's computer through a localarea network (LAN) or a wide area network (WAN), or the connection maybe made to an external computer (for example, through the Internet usingan Internet Service Provider).

Many different embodiments have been disclosed herein, in connectionwith the above description and the drawings. It will be understood thatit would be unduly repetitious and obfuscating to literally describe andillustrate every combination and subcombination of these embodiments.Accordingly, all embodiments can be combined in any way and/orcombination, and the present specification, including the drawings,shall be construed to constitute a complete written description of allcombinations and subcombinations of the embodiments described herein,and of the manner and process of making and using them, and shallsupport claims to any such combination or subcombination.

Abbreviations that may be used in the preceding description include

ABBREVIATION EXPLANATION

3GPP 3rd Generation Partnership Project

ACK Acknowledgement

BSR Buffer Status Report

CN Core Network

CU Central Unit

CP Control Plane

DL Downlink

DU Distributed Unit

IAB Integrated Access Backhaul

MAC Medium Access Control

NACK Negative ACK

PDCP Packet Data Convergence Protocol

PDU Protocol Data Unit

RLC Radio Link Control

RRC Radio Resource Control

SIB System Information Block

SDU Service Data Unit

SR Scheduling Request

UP User Plane

UE User Equipment

UL Uplink

It will be appreciated by persons skilled in the art that theembodiments described herein are not limited to what has beenparticularly shown and described herein above. In addition, unlessmention was made above to the contrary, it should be noted that all ofthe accompanying drawings are not to scale. A variety of modificationsand variations are possible in light of the above teachings withoutdeparting from the scope of the following claims.

What is claimed is:
 1. A child integrated access backhaul (IAB) nodeconfigured to communicate with a first parent IAB node and a descendantIAB node over a backhaul network, the child IAB node comprising:processing circuitry configured to: detect a backhaul link failurebetween the child IAB node and the first parent IAB node; in response tothe detected backhaul link failure, cause transmission of a radio linkfailure indication to the descendant IAB node, the radio link failureindication being configured to cause each descendant IAB node in anestablished communication path receiving the radio link failureindication to modify data transmission and remain on the establishedcommunication path to the child IAB node; receive signaling indicatingfor the child IAB node to connect to a second parent IAB node; andmodify network topology at least in part by connecting to the secondparent IAB node.
 2. The child IAB node of claim 1, wherein the radiolink failure indication is a failure report that indicates at least oneof: a cause of the detected backhaul link failure; IAB nodeidentification; failure report identifier; backhaul link failure time;and results of measurements performed by the child IAB node.
 3. Thechild IAB node of claim 1, wherein the radio link failure indication isa failure report that includes results of measurements performed by thechild IAB node, the results of the measurements indicating at least onediscoverable parent IAB node.
 4. A method implemented by a childintegrated access backhaul (IAB) node that is configured to communicatewith a first parent IAB node and a descendant IAB node over a backhaulnetwork, the method comprising: detecting a backhaul link failurebetween the child IAB node and the first parent IAB node; in response tothe detected backhaul link failure, causing transmission of a radio linkfailure indication to the descendant IAB node, the radio link failureindication being configured to cause each descendant IAB node in anestablished communication path receiving the radio link failureindication to modify data transmission and remain on the establishedcommunication path to the child IAB node; receiving signaling indicatingfor the child IAB node to connect to a second parent IAB node; andmodifying network topology at least in part by connecting to the secondparent IAB node.
 5. The method of claim 4, wherein the radio linkfailure indication is a failure report that indicates at least one of: acause of the detected backhaul link failure; IAB node identification;failure report identifier; backhaul link failure time; and results ofmeasurements performed by the child IAB node.
 6. The method of claim 4,wherein the radio link failure indication is a failure report thatincludes results of measurements performed by the child IAB node, theresults of the measurements indicating at least one discoverable parentIAB node.
 7. A donor integrated access backhaul (IAB) node incommunication with a first parent IAB node, a child IAB node and atleast one descendant IAB node over a backhaul network, the first parentIAB node being in communication with the child IAB node and thedescendant IAB node, the donor IAB node comprising: processing circuitryconfigured to: receive a radio link failure indication from one of theat least one descendent IAB nodes, the radio link failure indicationindicating a radio link failure between the child IAB node and the firstparent IAB node, the radio link failure indication being configured tocause each descendant IAB node in an established communication pathreceiving the radio link failure indication to modify data transmissionand remain on the established communication path to the child IAB node;determine a second parent IAB node for the child IAB node to connect tobased at least in part on the radio link failure indication; and causetransmission of signaling to the child IAB node, the signalingindicating for the child IAB node to modify a network topology at leastin part by connecting to the second parent IAB node.
 8. The donor IABnode of claim 7, wherein the indication is a failure report destined fora donor IAB node, the failure report indicates at least one of: a causeof the radio link failure; IAB node identification; failure reportidentifier; backhaul link failure time; and results of measurementsperformed by the child IAB node.
 9. The donor IAB node of claim 7,wherein the radio link failure indication is a failure report includingresults of measurements performed by the child IAB node, the results ofthe measurements indicating at least one discoverable parent IAB node.10. A method implemented by a donor integrated access backhaul (IAB)node that is in communication with a first parent IAB node, a child IABnode and at least one descendant IAB node over a backhaul network, thefirst parent IAB node being in communication with the child IAB node andthe descendant IAB node, the method comprising: receiving a radio linkfailure indication from one of the at least one descendent IAB node, theradio link failure indication indicating a radio link failure betweenthe child IAB node and the first parent IAB node, the radio link failureindication being configured to cause each descendant IAB node in anestablished communication path receiving the radio link failureindication to modify data transmission and remain on the establishedcommunication path to the child IAB node; determining a second parentIAB node for the child IAB node to connect to based at least in part onthe radio link failure indication; and causing transmission of signalingto the child IAB node, the signaling indicating for the child IAB nodeto modify a network topology at least in part by connecting to thesecond parent IAB node.
 11. The method of claim 10, wherein the radiolink failure indication is a failure report destined for a donor IABnode, the failure report indicates at least one of: a cause of the radiolink failure; IAB node identification; failure report identifier;backhaul link failure time; and results of measurements performed by thechild IAB node.
 12. The method of claim 10, wherein the radio linkfailure indication is a failure report including results of measurementsperformed by the child IAB node, the results of the measurementsindicating at least one discoverable parent IAB node.
 13. A descendantintegrated access backhaul (IAB) node in communication with a donor IABnode via at least a first parent IAB node and a child IAB node over abackhaul network, the descendant IAB node comprising: processingcircuitry configured to: receive a radio link failure indication; inresponse to the radio link failure indication: modify data transmissionand remain on an established communication path to the child IAB node;and cause transmission of the radio link failure indication to the donornode; receive signaling from the donor IAB node, the signalingindicating for the child IAB node to modify network topology at least inpart by connecting to a second parent IAB node; and cause transmissionthe signaling to the child IAB node.
 14. The descendant IAB node ofclaim 13, wherein the processing circuitry is further configured to:determine whether an alternate communication path from the descendantIAB node to the donor IAB node is configured; and if the alternatecommunication path is configured, cause transmission of the radio linkfailure indication along the alternative communication path to the donorIAB node.
 15. The descendant IAB node of claim 13, wherein the radiolink failure indication is a failure report destined for a donor IABnode, the failure report including results of measurements performed bythe child IAB node, the results of the measurements indicating at leastone discoverable parent IAB node.
 16. A method implemented by adescendant integrated access backhaul (IAB) node that is incommunication with a donor IAB node via at least a first parent IAB nodeand a child IAB node over a backhaul network, the method comprising:receiving a radio link failure indication; in response to the radio linkfailure indication: modifying data transmission and remain on anestablished communication path to the child IAB node; and causingtransmission of the radio link failure indication to the donor IAB node;receiving signaling from the donor IAB node, the signaling indicatingfor the child IAB node to modify network topology at least in part byconnecting to a second parent IAB node; and causing transmission of thesignaling to the child IAB node.
 17. The method of claim 16, furthercomprising: determining whether an alternate communication path from thedescendant IAB node to the donor IAB node is configured; and if thealternate communication path is configured, causing transmission of theradio link failure indication along the alternative communication pathto the donor IAB node.
 18. The method of claim 16, further comprising:determining whether an alternate communication path from the descendantIAB node to the donor IAB node is configured; and if the alternatecommunication path is not configured, causing transmission of the radiolink failure indication to another descendant IAB node.
 19. The methodof claim 16, wherein the radio link failure indication is a failurereport destined for a donor IAB node, the failure report indicates atleast one of: a cause of the radio link failure; IAB nodeidentification; failure report identifier; backhaul link failure time;and results of measurements performed by the child IAB node.
 20. Themethod of claim 16, wherein the radio link failure indication is afailure report destined for a donor IAB node, the failure reportincluding results of measurements performed by the child IAB node, theresults of the measurements indicating at least one discoverable parentIAB node.